Apparatus for adjusting the suction slotin a drag suction dredger



June 2, 1970 A. HADJIDAKIS 3,514,881

APPARATUS FOR ADJUSTING THE SUCTION SLOT IN A DRAG SUCTION DREDGER Filed Oct. 6. 196'? INVENTOR AcH/LLEs IIAbd/DflK/S BY 17W ATTORNEYS United States Patent 3,514,881 APPARATUS FOR ADJUSTING THE SUCTION SLOT IN A DRAG SUCTION DREDGER Achilles Hadjidakis, The Hague, Netherlands, assignor to Mineraal Technologisch Instituut, Delft, Netherlands Filed Oct. 6, 1967, Ser. No. 673,515 Claims priority, application Netherlands, Oct. 6, 1966, 6614098 Int. Cl. E02f 3/92 US. Cl. 37-58 1 Claim ABSTRACT OF THE DISCLOSURE The invention relates to apparatus for adjusting the suction slot between the suction head of a drag suction dredger and the layer to be treated. It is known that the output of the suction head of a drag suction dredger depends upon the size of the suction slot, for the latter in combination with a number of other factors will determine the difference in pressure between the surrounding water and the interior of the suction head, and thus the rate of flow of the water through the slot. This stream of water loosens the sand and feeds it into the suction head, and the cutting action or loosening action of this stream of water through the slot is larger, and thus the output will also be larger, when the difference in pressure, and accordingly the rate of flow of the water, is great. The adjustment of the suction slot was hitherto effected imperfectly and only approximately, because as a rule on the suction head is present an adjustable member which, dependent upon the condition of the layer to be treated, is adjusted, when the suction pipe has been raised, in a given but fixed way, an adjustment, however, which can hardly approximate the ideal adjustment. The Dutch Pat. No. 107,749 describes a suction head provided with a leaf which rests with a supporting device on the bottom of the groove drawn, i.e. on a layer which has been equalized as much as possible by the preceding treatment, as a result of which the fixed adjustment of the rear of the suction head corresponds as much as possible to the subsoil, i.e. the height of the suction slot, once adjusted, remains approximately constant. However, when in this embodiment the supporting device sinks more or less deeply into the sand layer, even this arrangement is ineffective, even apart from the fact that only fixed adjustments are possible, which indeed allow of dilierent heights of the suction slot, but do not permit adaptation of this height to the treatment and an optimum height.

It is the object of the invention to furnish apparatus with which as high an output as possible can be achieved. This object is attained according to the invention by the feature that the means for adjustment of the suction slot reduce the latter, in dependence upon the pressure in the suction pipe, measured upstream of the pump, to a minimum value until the limiting value for the vacuum near the pump has been reached. According to the invention therefore a continuous adjustment of members determining the suction slot should be present, and this adjustment is controlled by the vacuum in the suction pipe near the pump in such a way that this adjustment Patented June 2, 1970 always aims at a minimum height of the suction slot, but stops this as soon as the limiting value for the vacuum near the pump has been reached. When the limiting value is exceeded, cavitation or stalling of the pump may occur, which may result in that the transport through the suction pipe stops and a change may take place. This limiting value must not therefore be exceeded. But according as the vacuum near the pump approaches the limiting value the difference in pressure over, and thus the output of, the suction head also increases, so that when the suction slot is controlled in dependence upon this limiting value, for the vacuum near the pump, a maximum output can be achieved.

According to the invention a safety device may be provided such that when this limiting value is exceeded, i.e. the vacuum increases to such an extent that the said drawbacks may occur, an enlargement of the suction slot takes place. This may be important when the sand is loosened irregularly.

The apparatus can be provided quite simply. Starting from an apparatus according to the Dutch Pat. No. 107,749, the supporting device may be connected with the suction head via a screwed spindle or a hydraulic cylinder. In the case of apparatuses supported in some other way, the suction head may be equipped with a member determining the slot, which member can be controlled by means of a pressure cylinder or a motor. The apparatus which causes the operation of the adjusting mechanism, e.g. the pressure cylinder, can be controlled by regulating pulses originating from a vacuum gauge, which is present in the suction pipe at a point just upstream of the pump.

If dredging takes place on a sloping soil, so that the suction head comes to lie deeper and deeper with respect to the ship, this has the consequence that the change in depth-position of the suction head entails a change of the static lift, and the latter naturally affects the difference in pressure between the interior and the exterior of the suction head. The limiting value for the vacuum measured upstream of the pump is determined only by the properties of the pump. Because according to the invention the vacuum and the adjustment of the height of the suction slot are coupled, it is ensured at the same time that with a change of the depth at which the suction pipe is located, and the corresponding change of the static lift, also an automatic correction of the height of the suction slot takes place. In other words, a greater depth the suction slot will be larger than at a lesser depth. Thus it is possible to achieve an optimum output with varying drafts.

The invention now will be further elucidated with reference to the drawing which diagramatically discloses the principle of the invention, leaving out, for clearness sake, details which are known in the art.

The drawing shows a suction pipe 1 supported by a vessel, not shown, and provided with a suction pump 2. At the lower end of pipe 1, a suction head 3 has been provided with an adjustable leaf 4 having a pivotal connection with the suction head at 5. Between a bracket 6 on the suction head and a bracket 7 on the leaf, a hydraulic cylinder 8 has been provided having its piston rod pivotally connected with the bracket 7 and its cylinder with the bracket 6.

Conduits 9 and 10 connect the cylinder 8'with a slide valve having a slide 11. This slide is shown in its intermediate position in which there is no supply of hydraulic fluid to the cylinder 8. The drawing shows a reservoir 12, a pump 13, and a return conduit 14.

The slide is operated by leftand right-hand solenoids, 15 and 16 provided with springs 17 and 18, respectively, for returning the slide to the intermediate position.

If the right-hand solenoid 16 is energized, the slide moves to the right in the drawing which means that the connection shown in the left-hand portion of the slide 11 is obtained. Accordingly the pump 13 feeds liquid under pressure into the conduit 10 with the result that the leaf 4 is raised and accordingly the suction slot 19 is enlarged.

If the solenoid 15 is energized, the slide moves to the left providing the connection shown in the right-hand portion of the slide. In that case, liquid under pressure is fed into the conduit 9 with the result that the leaf 4 is moved downwardly to reduce the slot 19.

Upstream of the pump 2 the pressure in the suction pipe 1 is measured by the vacuum transducer 20. This is an instrument having a membrane provided with a number of strain gauges which are connected in electrical circuit with the control device 21 having a pointer 22 which indicates on the scale 23 the value of the vacuum existing in the tube 1 upstream of the pump 2.

On the scale are two adjustable marking members 24 and 25. Within the area defined by said marking numbers 24 and 25, the suction in the suction pipe 1 has the right value and there is no need for adjustment of the suction slot.

The pointer 22 operates contacts related to the marking elements 24, 25. This can be done for example by means of light beams interrupted by the pointer 22. In the drawing it is assumed that the pointer 22 makes contact with the marking elements 24 and 25. If the pointer moves to the right, corresponding to an increase of the vacuum, it will contact and pass the marking element 25 with the result that the solenoid 16 is energized moving the valve to the right, in which position the leaf 4 is raised to increase the slot 19 and accordingly reduce the vacuum. This reduction will return the pointer.

As long as the vacuum is too low there will be contact between the pointer 22 and the marking element 24 and accordingly the solenoid 15 will be energized with the result that the slide 11 moves to the left and the leaf 4 then will be moved downwardly to reduce the slot 19 and accordingly increase the vacuum in the suction pipe 1.

Having described my invention, I claim: 1. A drag suction dredger comprising a suction head that passes across and sucks up material from a layer to be treated, a pump for creating said suction, a suction pipe interconnecting said pump and said suction head, said suction head comprising a member mounted on the head for vertical swinging movement about a horizontal axis toward and away from the layer to be treated to change the vertical distance between the suction head and the layer to be treated, and means responsive to the pressure in said suction pipe between the suction head and the pump outside a predetermined pressure range to move said member vertically relative to said layer to be treated and relative to said suction pipe in a direction to return the pressure in said suction pipe to a value within said range, said responsive means comprising fluid pressure means for moving said member vertically, valve means for selectively directing fluid pressure to said fluid pressure means thereby to move said member in a selected vertical direction, a pair of solenoids for moving said valve means in opposite directions, a member movable as a function of pressure in said suction pipe, and a pair of spaced means for individually operating each of said solenoids, the last-named member being movable between said spaced means over said predetermined pressure range and being adapted to actuate one of said solenoids upon registry with one of said solenoid operators.

References Cited UNITED STATES PATENTS 1,250,276 12/1917 Brown et a1. 37-58 1,754,746 4/1930 Ewig 3758 3,111,778 11/1963 Fonnesbeck 3758 3,224,121 12/1965 Denning 3758 FOREIGN PATENTS 873,734 7/1961 Great Britain.

ROBERT E. PULFREY, Primary Examiner C. D. CROWDER, Assistant Examiner US. Cl. X.R.C. 

